KR100893131B1 - Method of fabricating nitride semiconductor and method of fabricating semiconductor device - Google Patents

Abstract

The present invention provides a method for producing a nitride semiconductor and a method for manufacturing a semiconductor device using the same, which can lower the contact resistance with the electrode and improve the stability of the characteristics. After the nitride semiconductor to which the p-type impurity is added is produced, the surface is treated in an atmosphere containing active oxygen to remove carbon present on the surface, and an oxide film is formed. Thereafter, the p-type impurity is activated to be p-type. Since carbon on the surface is removed to form an oxide film, the surface of the nitride semiconductor can be prevented from deteriorating in the activation process, and the activation rate of the p-type impurity can be improved. Therefore, the contact resistance with an electrode can be made low and the nonuniformity of a characteristic can be made small.

Nitride semiconductor, semiconductor element, p-type impurity, manufacturing method.

Description

METHODS OF FABRICATING NITRIDE SEMICONDUCTOR AND METHOD OF FABRICATING SEMICONDUCTOR DEVICE

1 is a flowchart illustrating a method of manufacturing a nitride semiconductor according to one embodiment of the present invention.

2 is a cross-sectional view showing a process of a method of manufacturing a nitride semiconductor according to one embodiment of the present invention.

3 is a cross-sectional view showing the structure of a semiconductor laser fabricated using the method for producing a nitride semiconductor according to one embodiment of the present invention.

4 is a characteristic diagram showing a contact resistance and a voltage of a semiconductor laser according to Embodiment 1 of the present invention.

5 is a characteristic diagram showing contact resistance and voltage of a semiconductor laser according to Comparative Example 1 with respect to Example 1 of the present invention.

The present invention relates to a method for manufacturing a nitride semiconductor including a step of activating a p-type impurity and a method for manufacturing a semiconductor device using the same.

Nitride semiconductors such as GaN, AlGaN mixed crystals or AlInGaN mixed crystals are promising as constituent materials of light emitting devices capable of obtaining light emission from the visible region to the ultraviolet region or as constituent materials of electronic devices. Particularly, light emitting diodes (LEDs) using nitride semiconductors have already been put to practical use, and have attracted great attention. In addition, the realization of semiconductor lasers (LDs) using nitride semiconductors has also been reported, and application for the first time as a light source of an optical disk device is expected.

By the way, in order to acquire the outstanding characteristic in such an element, it is important to make ohmic contact with an electrode favorable with respect to a semiconductor, and to make contact resistance low. For example, with respect to n-type semiconductors, by adding n-type impurities such as silicon (Si), a relatively high carrier concentration can be obtained, and the electrodes can be easily brought into ohmic contact.

However, in the case of the p-type semiconductor, even if p-type impurities such as magnesium (Mg) are added, since they bind with hydrogen (H), the activation rate is low and only a carrier concentration of about 1 x 10 ¹⁸ cm ^-3 is obtained. . Therefore, it is difficult to make ohmic contact with an electrode satisfactorily, operation voltage becomes high, and there existed a problem that a nonuniformity tends to arise also in a characteristic.

The present invention has been made in view of the above problems, and an object thereof is to provide a method of manufacturing a nitride semiconductor capable of lowering a contact resistance with an electrode and a method of manufacturing a semiconductor device using the same.

The manufacturing method of the nitride semiconductor which concerns on the 1st aspect of this invention is a process of manufacturing the nitride semiconductor which added p-type impurity, the process of oxidizing the surface of the produced nitride semiconductor, and forming an oxide film, and forming the oxide film. Thereafter, the step of activating the p-type impurity to form the p-type.

Another method for producing a nitride semiconductor according to the second aspect of the present invention includes the steps of producing a nitride semiconductor to which p-type impurities are added, and treating the surface of the produced nitride semiconductor layer in an atmosphere containing active oxygen; After the surface of the nitride semiconductor is treated, p-type impurities are activated to form p-type.

The semiconductor device manufacturing method according to the third aspect of the present invention includes the steps of growing a nitride semiconductor layer containing p-type impurities, oxidizing the surface of the grown nitride semiconductor to form an oxide film, and forming an oxide film. After that, a step of activating the p-type impurity to form the p-type is included.

In another method of manufacturing a semiconductor device according to the fourth aspect of the present invention, a step of growing a nitride semiconductor layer to which p-type impurities are added and a step of treating the surface of the grown nitride semiconductor layer in an atmosphere containing active oxygen And after treating the surface of the nitride semiconductor layer, p-type impurities are activated to form p-type.

In the method of manufacturing the nitride semiconductor and the method of manufacturing the semiconductor device according to the present invention, since the surface of the nitride semiconductor is oxidized to form an oxide film before the p-type impurity is activated, or the surface of the nitride semiconductor contains active oxygen. Since the treatment is carried out in an atmosphere to prevent the deterioration of the surface of the nitride semiconductor in the activation treatment.

Embodiment of the Invention

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings.

1 is a flowchart illustrating a method of manufacturing a nitride semiconductor according to an embodiment of the present invention, and FIG. 2 is a flowchart illustrating a method of manufacturing a nitride semiconductor. The nitride semiconductor is at least one of the Group 3B elements of the short-period periodic table composed of gallium (Ga), aluminum (Al), indium (ln), boron (B), and the like, nitrogen (N) and arsenic. It means that it contains at least nitrogen in group 5B element of short-period periodic table which consists of (As), phosphorus (P), etc.

First, as shown in Fig. 2A, for example, M0CVD (Metal 0rganic Chemica1, Vapor Deposition; organometallic chemical vapor growth) on the c surface of the substrate 11 made of sapphire (α-Al ₂ O ₃ ). ), The nitride semiconductor 12 to which p-type impurities such as magnesium are added is grown and produced (step S101). The nitride semiconductor 12 contains a hydrogen atom, and activation of p-type impurities is inhibited by the bonding with hydrogen.

As a raw material for performing MOCVD, for example, trimethylgallium ((CH ₃ ) ₃ Ga) as a source gas of gallium, trimethylaluminum ((CH ₃ ) ₃ Al) as a source gas of aluminum, and a source of indium As the gas, for example, trimethylindium ((CH ₃ ) ₃ In), as the source gas of boron, for example trimethyl boron ((CH ₃ ) ₃ B), as the source gas of nitrogen, for example ammonia (NH ₃ ) use. As the source gas of magnesium, for example, bis = cyclopentadienyl magnesium ((C ₅ H ₅ ) ₂ Mg) is used.

Next, for example, if necessary, the surface of the nitride semiconductor 12 is washed with an organic solvent such as acetone to remove impurities adhering to the surface (step S102). Subsequently, for example, the surface of the nitride semiconductor 12 may be further cleaned by at least one of an acid and an alkali (step S103). The acid preferably contains hydrofluoric acid (HF), and the alkali preferably contains potassium hydroxide (KOH), sodium hydroxide (NaOH), ammonium hydroxide (NH ₄ OH), or the like.

Thereafter, as shown in FIG. 2B, the cleaned surface of the nitride semiconductor 12 is treated by irradiating ultraviolet rays in an atmosphere containing ozone (O ₃ ). Alternatively, the cleaned surface of the nitride semiconductor 12 is treated in a plasma atmosphere containing oxygen, such as an oxygen asher for plasma discharge in an atmosphere containing oxygen (O ₂ ). That is, the surface of the nitride semiconductor 12 is exposed to an atmosphere containing atomic oxygen, which is formed by dissociation of ozone or oxygen (step S104). As a result, the surface of the nitride semiconductor 12 is oxidized to form the oxide film 13, and at the same time, carbon (C) or organic matter which is not removed in the cleaning process existing on the surface of the nitride semiconductor 12 is removed. This is to prevent the surface of the nitride semiconductor 12 from being deteriorated in a subsequent process of activating the p-type impurity.

In particular, it is preferable to treat the surface of the nitride semiconductor 12 by irradiating ultraviolet rays in an ozone-containing atmosphere because the surface of the nitride semiconductor 12 is less damaged. At this time, it is preferable to perform this process for 1 minute or more in room temperature or more, for example.

In addition, the thickness of the oxide film 13 to be formed is preferably 5 nm or less. If the thickness is more than this, the activation rate decreases in the subsequent treatment of activating the p-type impurity, or the difficulty of the subsequent removal of the oxide film 13 increases. In addition, this oxide film 13 refers to what was intentionally formed, and does not mean the natural oxide film formed by being left in air.

After the oxide film 13 is formed, for example, the nitride semiconductor 12 is annealed at a temperature of 400 ° C or higher. As a result, hydrogen is released, and p-type impurities contained in the nitride semiconductor 12 are activated to be p-type (step S105). In the present embodiment, since the carbon present on the surface of the nitride semiconductor 12 is removed and the oxide film 13 is formed before the activation process, deterioration of the surface of the nitride semiconductor 12 in the activation process is prevented. do. In addition, it is thought that the release of hydrogen is promoted by the oxide film 13, and the activation rate of p-type impurities is improved.

After activation of the p-type impurity, as shown in Fig. 2C, for example, if necessary, the surface of the nitride semiconductor 12 is treated with at least one of an acid and an alkali, and the oxide film 13 Is removed (step S106). It is preferable to contain hydrofluoric acid as an acid, and it is preferable to contain 3% or more of potassium hydroxide, sodium hydroxide, ammonium hydroxide, etc. as an alkali. It is preferable to make processing temperature into 100 degrees C or less. The treatment may be either acid or alkali, but both are preferred. The order of treatment may be either acid or alkali.

As a result, a nitride semiconductor having a good interface with little deterioration and a high activation rate of p-type impurities is obtained.

Next, the manufacturing method of a semiconductor element using this manufacturing method of a nitride semiconductor, specifically, the manufacturing method of a semiconductor laser is demonstrated.

3 shows the configuration of a semiconductor laser manufactured using the method for producing a nitride semiconductor according to the present embodiment. First, for example, a substrate 21 made of sapphire is prepared, and each layer, which is an n-type nitride semiconductor layer, is grown on the c surface of the substrate 21 by MOCVD. That is, for example, an n-type contact layer 22 made of n-type GaN added with silicon as an n-type impurity, an n-type cladding layer 23 made of n-type AlGaN mixed crystal added with silicon, and n added with silicon The n type guide layer 24 made of type GaN is grown sequentially.

Subsequently, an active layer having a multi-quantum well structure in which a Ga _x In _1-x N (wherein 1? X? 0) mixed crystal layer having a different composition is laminated on the n-type nitride semiconductor layer, for example, by MOCVD method ( 25) grow.

After the active layer 25 is grown, each layer, which is a nitride semiconductor layer to which p-type impurities are added, for example, is grown on the active layer 25 by MOCVD. That is, for example, a current block layer 26 made of AlGaN mixed crystals containing magnesium, a p-type guide layer 27 made of GaN containing magnesium, and a p-type cladding layer 28 made of AlGaN mixed crystals containing magnesium. ), A p-type contact layer 29 made of GaN added with magnesium is sequentially grown.

Subsequently, the surface of the p-type contact layer 29 is washed with an organic solvent in the same manner as in the previous manufacturing method of the nitride semiconductor (FIG. 1; see step S102), and at least one of an acid and an alkali After washing (Fig. 1; see step S103), the resultant is treated in an atmosphere containing active oxygen to form an oxide film not shown in Fig. 3 (Fig. 1; see step S104).

After the oxide film is formed, it is included in the current block layer 26, the p-type guide layer 27, the p-type cladding layer 28, and the p-type contact layer 29 in the same manner as the method for manufacturing the nitride semiconductor described above. The resulting p-type impurities are activated to make those layers p-type (Fig. 1; see step S105). In the present embodiment, the active film is treated in an atmosphere containing active oxygen to form an oxide film, so that the surface of the p-type contact layer 29 is prevented from being deteriorated and the p-type contact layer 29 Carrier concentration becomes high.

After activating the p-type impurity, the oxide film is removed in the same manner as in the previous manufacturing method of the nitride semiconductor, by treatment with at least one of an acid and an alkali as necessary (Fig. 1; see step S106). Although this process does not need to be performed, it is preferable because the performed side can lower the contact resistance between the p-side electrode 31 and p-type contact layer 29 mentioned later.

After the oxide film is removed, a mask layer (not shown) is formed on the p-type contact layer 29, and the p-type contact layer 29 is formed using, for example, reactive ion etching (RIE) using the mask layer. ) And a portion of the p-type cladding layer 28 are selectively removed so that the upper portion of the p-type cladding layer 28 and the p-type contact layer 29 are thin band (ridge type). Subsequently, the mask layer (not shown) is removed, and the entire surface (that is, on the p-type cladding layer 28 and the p-type contact layer 29) is made of silicon dioxide (SiO ₂ ), for example, by vapor deposition. An insulating film 30 is formed. Subsequently, for example, a resist film (not shown) is coated on the insulating film 30, and the insulating film 30, the p-type cladding layer 28, and the p-type guide layer are formed using RlE as a mask. 27), a portion of the current block layer 26, the active layer 25, the n-type guide layer 24 and the n-type cladding layer 23 is selectively removed to expose the n-type contact layer 22.

After exposing the n-type contact layer 22, a resist film (not shown) is removed to form a resist film (not shown) on the entire surface (i.e., on the insulating film 30 and the n-type contact layer 22). Using the resist film as a mask, the insulating film 30 is selectively removed to expose the p-type contact layer 29. Thereafter, for example, palladium (Pd), platinum (Pt), and gold (Au) are selectively deposited sequentially on the entire surface (i.e., on the p-type contact layer 29 and a resist film not shown), The resist film (not shown) is removed together with the metal laminated thereon (liftoff) to form the p-side electrode 31. In this embodiment, since the surface of the p-type contact layer 29 is in a favorable state with little alteration, and the carrier concentration of the p-type contact layer 29 is improved, the p-type contact layer 29 and the p-side electrode ( 31) lowers the contact resistance.

After the p-side electrode 31 is formed, the entire surface (that is, on the n-type contact layer 22, the insulating film 30, and the p-side electrode 31) corresponds to the n-type contact layer 22. A resist film (not shown) having an opening is applied and formed. Thereafter, titanium (Ti), aluminum, and gold are sequentially deposited on the entire surface (i.e., on the n-type contact layer 22 and a resist film not shown), for example, by vacuum deposition. It is removed together with the metal formed above (liftoff) to form the n-side electrode 32.

Subsequently, after grinding the substrate 21 to a thickness of, for example, about 80 μm, the substrate 21 is cut to a predetermined size, and a pair of resonators opposing each other in the extending direction of the p-side electrode 31 is formed. A reflective film not shown is formed in the cross section. Thereby, the semiconductor laser shown in FIG. 3 is completed.

As described above, according to the present embodiment, before activating the p-type impurity, the surface of the nitride semiconductor 12 is treated in an atmosphere containing active oxygen to remove carbon present on the surface and to form the oxide film 13. Since it is possible to prevent the deterioration of the surface of the nitride semiconductor 12 in the activation process, the activation rate of the p-type impurity can be improved.                     

Therefore, by fabricating a semiconductor laser using this method, the contact resistance between the p-type contact layer 29 and the p-side electrode 3l can be lowered, the operating voltage can be lowered, and the variation in characteristics can be reduced. Can be.

Particularly, after activating the p-type impurity, treating with at least one of an acid and an alkali and removing the formed oxide film, the contact resistance between the p-type contact layer 29 and the p-side electrode 31 is better. It can be made low, and operation voltage can be made smaller.

EXAMPLE

In addition, specific embodiments of the present invention will be described in detail with reference to FIGS. 1 and 3.

Example 1

As Example 1, the some board | substrate 21 was prepared, and the semiconductor laser shown in FIG. 3 was produced with respect to each board | substrate 21 similarly to the manufacturing method of the semiconductor element demonstrated in Example.

In that case, the surface treatment before activating a p-type impurity was performed by irradiating an ultraviolet-ray for 10 minutes in 80 degreeC atmosphere containing ozone (FIG. 1; see step S104). Washing before surface treatment (FIG. 1; see step S102) was performed for 5 minutes, applying acetone using ultrasonic waves, and the washing | cleaning by acid and alkali was not performed (FIG. 1; see steps S10 and S103). The surface treatment after activating p-type impurity was performed by dipping for 5 minutes at 60 degreeC by the potassium hydroxide aqueous solution, and then immersing for 5 minutes at 50 degreeC with hydrofluoric acid (FIG. 1; see step S106). In addition, all manufacturing conditions were the same for each board | substrate 21. FIG.                     

With respect to the produced semiconductor laser, five pieces were appropriately selected from each of the substrates 21, and the contact resistance and voltage of the p-side electrode 31 when 50 mA of constant current flowed were measured, and the average value for each substrate was obtained. The result is shown in FIG.

As Comparative Example 1 of the present embodiment, except that the surface of the p-type contact layer 29 was not treated by irradiating ultraviolet rays in an atmosphere containing ozone, a plurality of substrates were provided in the same manner as in this embodiment. The semiconductor lasers were produced one by one, and in the same manner, the average values of the contact resistance and the voltage were obtained for each substrate. The result is shown in FIG. Moreover, in the comparative example 1, the board | substrate separate from Example 1 was prepared.

Example 2

In addition, as Example 2, two separate substrates 21 were prepared, and a plurality of semiconductor lasers were produced in the same manner as in Example 1 on the half side of each substrate 21. On the other half side, as Comparative Example 2, a plurality of semiconductor lasers which were not exposed in an atmosphere containing active oxygen were produced. Also regarding the semiconductor lasers of Examples 2 and 2, the contact resistance and voltage of the p-side electrode 31 at the time of passing a 50 mA current were appropriately selected by the number shown in Table 1 from each substrate 21. The standard nonuniformity of these average values and voltages was calculated | required. The obtained results are shown in Table 1.                     

TABLE 1

  Number of boards   Contact Resistance (Ω / cm)   Average value of voltage (V)   Standard deviation of voltage   Measure ()    Example 2 S ₃₅   0.0140    4.9    0.19    18 S ₃₆   0.0036    4.9    0.07    25    Comparative Example 2 S ₃₅   0.0340    5.8    0.11    14 S ₃₆   0.0370    5.5    0.52    30

As can be seen from FIG. 4, according to the first embodiment, the difference due to the difference in the substrate 21 in both the contact resistance and the voltage was small. On the other hand, as can be seen from FIG. 5, in Comparative Example 1, the difference in contact with the contact resistance and the voltage was large by the substrate. In other words, it was found that if the surface of the p-type contact layer 29 was treated in an atmosphere containing active oxygen before activating the p-type impurity, the variation in characteristics could be reduced and stabilized.

As can be seen from Table 1, in Example 2, the contact resistance and the voltage were both lower than those in Comparative Example 2. In other words, if the surface of the p-type contact layer 29 is treated in an atmosphere containing active oxygen before activating the p-type impurity, the contact resistance between the p-type contact layer 29 and the p-side electrode 31 is reduced. It turned out that it can be made low and it turned out that operation voltage can be reduced.

As mentioned above, although this invention was described based on embodiment and an Example, this invention is not limited to the said embodiment and Example, A various deformation | transformation is possible. For example, in the above embodiments and examples, the case where the oxide film is formed by treatment in an atmosphere containing active oxygen has been described, but the oxide film may be formed by another method.

In the above embodiments and examples, the oxide film is removed immediately after activation of the p-type impurity. However, the oxide film may always be removed before forming the p-side electrode, and the oxide film is removed immediately before forming the p-side electrode. It is preferable that the contamination of the surface of the p-type contact layer is small.

In the above embodiments and examples, a method of manufacturing a semiconductor laser has been described with a specific example as a method of manufacturing a semiconductor device, but the present invention can also be applied to the case of manufacturing other semiconductor devices such as an electric field transistor. In the above embodiments and examples, the case where the p-side electrode is formed in the p-type contact layer, which is the nitride semiconductor layer to which the p-type impurity is added, has been described. However, the present invention provides the nitride semiconductor layer to which the p-type impurity is added. The present invention can be widely applied in the case of forming an electrode which needs to be in ohmic contact.

In the above embodiments and examples, the case where the nitride semiconductor is formed by the MOCVD method has been described, but other methods such as a molecular beam epitaxy (MBE) method, a hydride vapor phase growth method, or a halide vapor phase growth method, etc. It may also be formed by a method. The hydride vapor phase growth method refers to a vapor phase growth method in which hydride (hydrogen) contributes to the reaction or transportation of source gas. The halide vapor phase growth method refers to a method in which halide (halide) contributes to the reaction or transportation of source gas. Meteorological growth law.

In the above embodiments and examples, a substrate made of sapphire is used, but a substrate made of another material such as GaN or SiC may be used.

As described above, according to the method of manufacturing the nitride semiconductor of the present invention or the method of manufacturing the semiconductor device, the surface of the nitride semiconductor is formed by oxidizing the surface of the nitride semiconductor and forming an oxide film before activating the p-type impurity. Since the treatment is performed in an atmosphere containing active oxygen, it is possible to prevent deterioration of the surface of the nitride semiconductor in the activation treatment and to improve the activation rate of the p-type impurity. Therefore, when the electrode is in ohmic contact with the nitride semiconductor, the contact resistance can be lowered and the operating voltage can be lowered.

In addition, according to the method of manufacturing the nitride semiconductor or the method of manufacturing the semiconductor device of the present invention, since the p-type impurity is activated, the oxide film is removed or treated by at least one of an acid and an alkali. Can be made lower than, and the operating voltage can be made lower.

     Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and those skilled in the art may add various modifications and changes without departing from the spirit and scope of the present invention. It will be appreciated. It is apparent that such modifications and variations are included in the following claims.

Claims (16)

delete delete manufacturing a nitride semiconductor to which p-type impurities are added; Oxidizing the surface of the produced nitride semiconductor to form an oxide film; Forming an oxide film and then activating the p-type impurity to form the p-type Including, And activating the p-type impurity, followed by removing the oxide film. manufacturing a nitride semiconductor to which p-type impurities are added; Oxidizing the surface of the produced nitride semiconductor to form an oxide film; Forming an oxide film and then activating the p-type impurity to form the p-type Including, After manufacturing the said nitride semiconductor and before forming an oxide film on the surface, the manufacturing method of the nitride semiconductor further includes the process of washing the surface of the said nitride semiconductor with an organic solvent. delete manufacturing a nitride semiconductor to which p-type impurities are added; A step of treating the surface of the produced nitride semiconductor in an atmosphere containing active oxygen, Treating the surface of the nitride semiconductor and then activating the p-type impurity to make the p-type Including, and activating the p-type impurity, and then treating the surface of the nitride semiconductor with at least one of an acid and an alkali. manufacturing a nitride semiconductor to which p-type impurities are added; A step of treating the surface of the produced nitride semiconductor in an atmosphere containing active oxygen, Treating the surface of the nitride semiconductor and then activating the p-type impurity to make the p-type Including, After manufacturing the said nitride semiconductor, and before processing in the atmosphere containing active oxygen, the method of manufacturing the nitride semiconductor further includes the process of washing the surface of the said nitride semiconductor with an organic solvent. delete delete growing a nitride semiconductor layer containing p-type impurities; Oxidizing the surface of the grown nitride semiconductor layer to form an oxide film, Forming an oxide film and then activating the p-type impurity to form the p-type Including, and activating the p-type impurity, and then removing the oxide film. The method of claim 10, And removing the oxide film, and then forming an electrode with respect to the p-type nitride semiconductor layer. growing a nitride semiconductor layer containing p-type impurities; Oxidizing the surface of the grown nitride semiconductor layer to form an oxide film, Forming an oxide film and then activating the p-type impurity to form the p-type Including, And growing the nitride semiconductor layer and then cleaning the surface of the nitride semiconductor layer with an organic solvent before forming an oxide film on the surface thereof. delete growing a nitride semiconductor layer containing p-type impurities; Treating the surface of the grown nitride semiconductor layer in an atmosphere containing active oxygen, Treating the surface of the nitride semiconductor layer and then activating the p-type impurity to make the p-type Including, and after activating the p-type impurity, treating the surface of the nitride semiconductor layer with at least one of an acid and an alkali. The method of claim 14, And a step of forming an electrode for the p-type nitride semiconductor layer after treating the surface of the nitride semiconductor layer with at least one of an acid and an alkali. growing a nitride semiconductor layer containing p-type impurities; Treating the surface of the grown nitride semiconductor layer in an atmosphere containing active oxygen, Treating the surface of the nitride semiconductor layer and then activating the p-type impurity to make the p-type Including, And growing the nitride semiconductor layer and then cleaning the surface of the nitride semiconductor layer with an organic solvent before treating it in an atmosphere containing active oxygen.

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